Cold hardiness & minimum temperature

Is Water Forget-me-not (Myosotis scorpioides)cold hardy? Hardiness zone & min temp

Also called Water Forget-me-not, True Water Forget-me-not, Scorpion Grass.

More about water forget-me-not

About Water Forget-me-not

Myosotis scorpioides · also called Water Forget-me-not, True Water Forget-me-not · flowering

Water Forget-me-not is a delightful native European perennial producing a long succession of tiny, sky-blue flowers with yellow eyes from May to September along stream banks, pond margins, and in boggy ground — one of the longest-flowering native marginal aquatics. Its creeping stems root at the nodes, forming a mat of soft, hairy, lance-shaped leaves that spread across the water surface. A magnet for bees and hoverflies and an excellent wildlife pond plant. Not listed as toxic to cats or dogs by the ASPCA.

Cold limit: USDA 5-9 · RHS H6 (-20 to 25°C)

What water forget-me-not's hardiness rating actually means

Yes — water forget-me-not is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 5-9 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −20 to −15 °C. Water Forget-me-not is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for water forget-me-not as it gets too cold:

It tolerates winter lows to about −20 to −15 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can water forget-me-not go outside or overwinter — and where?

Plant it out within USDA 5-9 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when water forget-me-not can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Water Forget-me-not hardiness — frequently asked questions

Is water forget-me-not cold hardy?

Yes — water forget-me-not is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Water Forget-me-not is hardy across USDA 5-9; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature water forget-me-not can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Water Forget-me-not is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is water forget-me-not?

Water Forget-me-not is rated USDA 5-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can water forget-me-not survive winter outside?

Plant it out within USDA 5-9 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to water forget-me-not below its minimum temperature?

It tolerates winter lows to about −20 to −15 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.